1. Field of the Invention
The present invention relates to the connection of optical and electrical components on an integrated package and particularly the electrical interconnection of optical components to electrical components.
2. Technical Background
As optical fibers increase in their use in communication systems, there is an ever increasing need for a higher degree of integration of optical components and electrical components in fiber optic applications. Also, the components themselves have become increasingly complex. Conventional wire interconnections typically employ gold wires having a diameter from 25 to 33 micrometers (.mu.m) connecting electrical lines of, for example, a planar lightwave circuit to the pin connections for the package. The mechanical resonant frequency of a wire of, for example, 25 micrometers in diameter and 2.5 mm in length is approximately 2.2 kHz. Quality control tests, such as the Bellcore qualification test, requires vibration testing in the frequency range of from 10 Hz to 2 kHz. With relatively long wires of the prior art, as the resonant frequency is approached or reached, there is a tendency for the wire bonds to break loose due to vibration, thereby causing failure of the packaged component. In order to alleviate this problem, the length of interconnecting conductors have been shortened to approximately 1 mm to raise the resonant frequency of such conductors to about 5 kHz. This technique of the prior art is known as "stitching" and, although reducing or eliminating the failure of components due to vibration, it increases the number of bonds as well as requiring island pads for the interconnection of series coupled shorter conductors.
Another approach in connection optical components to electrical components is the use of feed lines which are conductors printed on a substrate extending across a package. For components such as a thermal-optic 8.times.8 switch can result in over 200 electrical connections. The lines must have a size sufficient to maintain their resistance relatively low in order to avoid parasitic heating while at the same time there must be sufficient spacing between adjacent lines to prevent electrical cross talk. These factors lead to the consumption of a considerable amount of the surface area of a package, and, while reducing some of the problems inherent with separate electrical conductors, the use of parallel feed lines does not result in a compact hybrid package.
There exists a need, therefore, for packaging technique and structure for optical/electrical devices in a single package which alleviates the problems with wire bonds and connection techniques of the prior art.